Wanted: SIMH VMS quick test

Al Kossow aek at bitsavers.org
Tue Dec 16 11:58:59 CST 2014

On 12/16/14 9:39 AM, Chuck Guzis wrote:
> On 12/16/2014 06:29 AM, Al Kossow wrote:
>> On 12/15/14 9:04 PM, Chuck Guzis wrote:
>>> Okay, I've been working with my SCSI tape stuff and I'd like someone
>>> to check a .TAP image on a VAX VMS SIMH setup.
>> I looked at it with my tools. There are THREE extra bytes at the end of
>> the first record, before the 50 00 00 00.
>> Bob may pad to a short, but I don't think he pads to a long. The images
>> I create don't pad a record at all, what
>> you see is what you get.
>> Looks like VMS Fortran 4.5
> http://simh.trailing-edge.com/docs/simh_magtape.pdf is the document that I'm using for this.  I clearly have some extra padding in the records--that's a bug in my own padding routine.
> The document does say that records will be padded to an even byte boundary--is this incorrect?

No, if that's the format you want to support. I personally think it is incorrect since that wasn't what
was written on the tape.

> If I were to append a metadata record at the end of the image, would this hurt anyone?  Perhaps preceded by 4 tapemarks?

He added an end of media tag. I'd put it after that and wrap your record in block marks with an obvious ID string at the front

There should also be a magic number and a byte offset and at the very end of that last record so that you can lseek -8*3 bytes from the
end, find out the metadata is there and lseek to the start of it.

John Bordynuik defined bad block information in the tape images he created. Too bad it was never documented.

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